This invention relates in general to processes for reclaiming rubber-to-metal bonded material. In particular, the invention relates to a process for using flame heat to remove rubber from parts where the rubber is bonded to a metal component while leaving the metal component in a reusable state, and preferably with the rubber component substantially unaltered.
When rubber is bonded to metal through any of various conventional methods, the resulting bond often will not release, even when the rubber undergoes tearing or splitting. Thus, if a part is rejected after the bonding process, the whole part is often discarded. This is undesirable since the metal components are usually more costly to prepare than the rubber parts. Also, the rubber portion of the part often wears out while the metal portion is still perfectly usable. In either case, the expensive metal part is simply discarded along the rubber.
There are numerous methods known for recycling structures having bonded rubber and metal parts that separate the rubber from the metal. The methods vary widely in principle, from grinding and destructive heating to cryogenic freezing and chemical disintegration. In every case, either the metal or rubber component (or both) are dramatically affected.
U.S. Pat. No. 3,670,969, issued to Terada on Jun. 20, 1972, discloses a method of removing insulation from electrical wiring by chopping the wire into short sections, then dumping the pieces into a liquid-filled tank. The liquid with the cut up pieces is stirred by a special agitator designs to knock or chop the softer insulation off the wire. The specific gravity of the liquid is chosen so that the insulation knocked off the wire will float to the top of the liquid, while the wire will sink.
U.S. Pat. No. 4,342,647, issued to McMillan et al. on Aug. 3, 1982, teaches the removal of rubber from metal parts by bathing the parts in cryogenic liquid, during which the rubber becomes sufficiently embrittled that it can simply be removed by hammer milling. The rubber's properties undergo dramatic change as a result of cryogenic freezing. Also, the equipment required for handling the cryogenic liquid is relatively expensive and complex.
U.S. Pat. No. 5,234,171, issued to Fantacci on Aug. 10, 1993, discloses a method of grinding up vehicle tires and the like, whereupon the metal and rubber are separated by conventional magnetic separation and air classification. Obviously, the metal pieces are no longer in their original form and must be smelted down and recast or forged before being used again.
Finally, U.S. Pat. No. 5,505,008, issued to Hugo et al. on Apr. 9, 1996, discloses removal of organic materials from metal by subjecting the organic material to heat in a non-reactive atmosphere (to avoid combustion) for long enough that the organic material becomes brittle and either falls off or can easily be physically removed. While the metal workpiece is not significantly affected, the rubber piece will be destroyed.
None of the previously methods can satisfactorily reclaim workpieces made of rubber and metal bonded together, because they require physical or chemical destruction of either the metal or rubber portions, or both. A need remains for a method of separating bonded metal-rubber parts such as metal insert O-rings while leaving both the metal and the rubber portions in reusable form.